1. Field of the Invention
The invention relates to a hydraulic elevator.
2. Discussion of the Prior Art
Elevators of this type are already known. They can be classified into three different types of construction, depending on how the elevator car is fastened to the hydraulic jack.
A common arrangement is for the car to rest on a platform on the end face of the jack. A disadvantage of this configuration is the large amount of space required by the retracted jack. In addition to this arrangement with the jack under the car, there is the so-called rucksack arrangement, in which the jack passes behind the car and acts on the upper part of a frame which carries the car. The point of attachment is defined by the prescribed height of the upper part of the frame. Consequently, depending on the type of car and the specified height of attachment to the upper part of the frame, a jack with a correspondingly long cylinder is required. In some cases an additional extension to the cylinder is used for this purpose, or an extra long cylinder is chosen, to meet the requirements for attachment.
Finally, the third type of construction is disclosed in the unexamined German patent application DE-OS 2062161. With this arrangement, a supporting framework and the car together form a self-contained module which is pre-assembled and needs only to be placed in position at the installation location. Two guide rails at the sides are joined together at their upper ends by means of a crossbeam to form the supporting framework. The upper ends of two telescopic jacks are attached to the crossbeam, while the lower ends of the telescopic jack are fixed at the car. The jacks are accommodated together with the guide rails in recesses on opposite sides in the car walls. The pistons of the jacks are fixed rigidly to the crossbeam, and the lower ends of the cylinders are bolted to lateral projections from the floor of the car. As the piston is fastened to the crossbeam, the cylinder and the car fastened to it rise when pressure is applied.
Although this type of hydraulic drive for elevators avoids the need for hollowed out spaces below the floor of the lowest landing, and long overtravel at the upper end of the hoistway, it nevertheless has the disadvantage that it is only suitable for elevator installations with a limited travel height. The hydraulic jacks are also especially costly, as it is essential for their cylinders to be at least as long as the intended hoisting distance.